The UK Border Agency has apologised after an email was mistakenly sent to Customs officers at the UK's busiest airport advising them not to search potential drug smugglers.
The Sun newspaper reported that the message was sent due to a lack of staff at Heathrow Airport for three days during the Christmas period.
The email issued by the UKBA and seen by the paper reads: "We would seek your co-operation in managing this situation by asking that you do not actively seek to identify any passenger with internal concealments for three days up to and including Christmas Day."
The UKBA has insisted that the email should never have been sent.
A Border Agency source said: "As soon as the email was sent, phone calls started to try and rectify the situation."
Heathrow is one of the world's busiest airports and routinely handles around 70 million passengers per year.
The UKBA are now expected to launch a review into the incident.
Jonathan Sedgwick, deputy chief executive of the UK Border Agency, said: "This email should never have been sent as this approach does not represent UKBA policy.
"Our aim is to prevent and detect the smuggling of drugs however people try to bring it into the country.
"Our drug enforcement teams have worked tirelessly over the Christmas period and have successfully intercepted several shipments of class A drugs.
"We need to review what has happened here to ensure that this situation does not arise in the future."